Hans Kristian Rausing, one of the heirs to to the multibillion pound Tetra Pak packaging dynasty, has been arrested in connection with the death of his wife Eva, after her body was found at their luxurious west London home.

The Metropolitan police said a body had been found at an address in Cadogan Place, Belgravia, one of the most exclusive streets in London.

The property had been searched following the earlier arrest in south London of a 49-year-old man on suspicion of possession of drugs, a spokesman said. The man was later rearrested in connection with the death, which is being treated as "unexplained". He is being held at a station in south London.

Though Scotland Yard has not yet confirmed his identity, the 49-year-old is understood to be Rausing, whose Swedish grandfather Ruben Rausing invented the Tetra Laval milk carton in the 1960s. His father Hans senior was ranked by Forbes in 2010 as the 64th richest man in the world.

A post mortem was opened at 1pm on Monday at Westminster mortuary. The dead woman has not yet been formally identified, but sources confirmed the body was that of Mrs Rausing.

The five storey terraced house is in one of London's most expensive areas just off Sloane Street, between Knightsbridge and Chelsea. Officers could be seen guarding the front door last night, which was taped off.

The couple, who have four teenage children, have struggled for many years with addiction to hard drugs, narrowly escaping prison in 2008 after heroin and £2,000 worth of crack cocaine were found at their home. Mrs Rausing had been arrested after trying to smuggle several wraps of cocaine into a reception at the American embassy in Grosvenor Square.

As part of their caution, the couple were required to attend a four-month drugs rehabilitation programme, and they were prominent benefactors of a number of anti-drugs charities, even while they continued to struggle with their own addictions.

The American-born Mrs Rausing, the daughter of a wealthy Pepsi executive, met her husband in the 1980s when they were both being treated at a US drug rehabilitation centre.

In a statement following her arrest in 2008, she said: "I have made a serious mistake which I very much regret," she said. "I intend to leave as soon as possible to seek the help that I very much need. I have made a grave error and I consider myself to have taken a wrong turn in the course of my life. I am very sorry for the upset I have caused. I thank my family and friends for their kindness and understanding."

After the hearing, the Rausing family said they "hope[d] with all their hearts" that the couple could "overcome their addiction", and that they would support them.

But the decision to drop charges in favour of a conditional caution attracted some criticism of double standards for wealthy offenders, and was described as "very surprising" by the then Metropolitan police commissioner Sir Ian Blair who said it "sends entirely the wrong message about drug use and disregards the harm it does to communities." He added that the decision not to prosecute "reminds me of the 19th-century legal comment often attributed to Sir James Mathew: 'In England justice is open to all - just like the Ritz.'"

Though he was born into relatively modest middle-class circumstances in Sweden, Hans Kristian Rausing's life was transformed by the vast wealth generated by his grandfather's packaging invention, which permitted milk to be kept fresh without the need for refrigeration.

His father Hans Sr moved the family to Britain in the 1980s to avoid Sweden's higher tax regime, and in 1996 sold his half of the Tetra Pak company to his now late brother Gad for almost £5bn. The company is now controlled by Gad's three children, Jorn, Finn and Kirsten, who remain based in Sweden. Hans Sr, now in his 80s, lives in a 900-acre East Sussex estate, where he raises deer and collects vintage cars and is thought to have a personal fortune worth almost £6bn.

Hans Kristian has two sisters, the older of whom, Lisbet, studied at Berkeley and Harvard and went on to be a research fellow at Imperial College. Sigrid Rausing, his other sister, owns the literary magazine Granta and the publishing firm Portobello books, and is a noted philanthropist.

In an interview in 2004, she said great wealth was something that was not always easy to come to terms with: "Be open about it and be active with it." She has said that her philanthropic habit developed partly from guilt, "but I think it was probably shame, if I can make that distinction. People knew you had money, so you could never say, 'Come back next month.'"

Eva and Hans Kristian Rausing were also philanthropists, supporting, among others, charities working in the arts, sport and anti-addiction charities. Mrs Rausing was even a patron of one charity, The Mentor Foundation, which worked to help people out of addiction and also boasts the Queen of Sweden, Queen Noor of Jordan and Prince Talal Bin Abdul Aziz Al Saud of Saudi Arabia as honorary trustees.

Prince Charles, with whom Hans K Rausing is said to be on first name terms, has described him as "a very special philanthropist" because of his support for drugs charities.